Process of producing by-products from waste pickle liquor.



A. F. HOFFMAN.

PROCESS 0F PRODUCING BY-PRODUCTS FROM WASTE PICKLE UQLIOR.

APPLICATION FILED APR` 8.1916. HENEVVLD NOVy l0. 91?.

luvntwl Junv Il, i918.

STATES PATENT OFFICE.

ADDISON F. HOFFMAN, 0F PITTSBURGH, PENNSYLVANIA PROCESS 0F `PROIDUGIN G :BY-PRODUCTS FROM WASTE PIGKLE LIQUOR.

Application led April 8, 1916, Serial No. 89,886.

? MAN, a citizen of the United States, residing atrPittsburgh, in the county vof Alle- 5 Jgheny and State of Pennsylvania, have invented new and useful Improvements in Process of Producing By-Produots from Waste Pickle Liquor, of which the following is a specification. Y

The present invention relates to the recovery of by-products, particularly pigments and sulfuric or other acid fromwaste pickle liquor, and` with the consequent elimination of serious disadvantages which have hitherto resulted from dumping these waste liquors into streams.

At present there are three pickling solutions in common use, for the pickling of iron articles, previous to tinning, galvanizing and the like, these solutions consisting respectively of sulfuric acid and Water, hydrochloric acid andjwater, and sulfuric'acid, sodium' bisulfate and water. All three of these liquors contain more or less free acid when discharged from the pickling tanks, and also contain large quantities of iron salts. It is the usual practice to withdraw the pickling liquor from the pickling tanks when the action of the liquor on the iron articles slows down, to then add more or less strong acid thereto, to bring the pickle liquor up to normal stre gth of acid, and then to reuse the piclile liquor. This strengthening of the old liquors is repeated in practice several times, until the liquor becomes relatively concentrated in iron salts, after which it would not be advantageous to Vadd further quantities `of acid, since the presence of the Ilargeamounts of iron salts is detrimental in the pickling operation.

The present invention comprises the treatment of waste pickle liquors including and having particular reference to the concentrated solutions of iron salts, which cannot be profitably strengthened by addition of acid and reused inthe ickling operation. -The accompanying rawing shows diagrammatically a device for carrying out the process of my present invention.

1 shows a icklin tank of any desired construction, om w ich the pickle li uor, while still substantially boiling hot," ows through a pipe into a settling and clarifyl 65 ingtank 2, which is preferably placed un- ,derground, in order t0 economze space,

Specification of Letters Patent.

Patented J une 11, 1918.

Renewed November 10, 1917. Serial No. 201,401.

and also in order to retain the heat in the liquor. The liquor is here allowed to settle and clarify, and while scrap iron may be added in this tank if desired, it is ordinarily not advisable to add scrap iron. In this tank all dissolved gases have .a chanceto escape from the liquor. The clarified liquor is then drawn into tank 3 by opening the valve connecting these two vessels, and in the tank 3 there is added to the liquor pulverized magnesite or pulverized dolomite, although for certain purposes pulverized limestone may be employed, but limestone is less advantageous as will appear farther on. A sulicient amount of this material being added to neutralize all free acid and to convert the soluble iron salts into hydroxids should preferably be added. The following reactions take place:

The presence of magnesium carbonate in the alkaline material employed is a distinct advantage in producing a pigment, since the magnesium sulfate 1s readily soluble and does not appear in the precipitate. The solution of magnesium sulfate left after the removal of the precipitate may be concentrated and magnesium sulfate produced as a by-product. In some ades of magnesite and dolomite a considera le amount of magnesium silicate is found which likewise reacts with the iron salts, although more slowly. In cases of waste pickle liquors from the h drochloric acid pickling processes, the fo owing are the typical reactions:

The sludge in tank 3 is then pumped up by the pump 4 into the tank 5, where the surplus liquid may be drawn oif for further treatment. In the tank 5 the liquid may be heated to the boiling point and allowed to cool, in'order to remove dissolved gases and i perature of preferably about 300 i C.

to aid in the precipitationand separation ofy the precipitate from the llquor. The liquor and precipitate may if desired be passed' The precipitate is then calcined, for example in the rotary calciner 9, at a temat which temperature the water is completely drivenfofl" with the production of ferric oxid, Vthe color of the product depending to some extent upon the time of burning, temperature of burning, quantity of-foreign matter present, and other conditions. Accordingly, it is advisable to carefully regulate the temperature of the calcining `operation.

During the calcining operation, the major portion of whatever calcium sulfate may be present is reduced, by the reducing ame used in .the heating o eration, to calcium 'sulfite or calcium su d, which materials may be readily leached out of the calcined product, by means of water containing small amounts of hydrochloric or sulfuric acid. This completely removes the calcium sulfate, thereby greatly improving the character of the pigment, and the dilute acid does `greatly injure lthe color of the pigment.`

Lime is further not to be recommended, on account of increased cost. What I claim and'desire to secure by Letters Patent is:

A process of treating waste pickle liquor which comprises settling the hot liquor, adding a calcareous neutralizing agent in amount capable of neutralizing all the free acid therein, without previously reducing .the ferrie salts contained therein, and a sufficient excess of such neutralizing agent to convert the soluble iron salts into hydroxids, said neutralizing agent containing compounds of magnesium capable of neutralizing acids, thoroughly agitating the mixture, and allowing the same to settle, separating the sludge from the liquid, drying and aeratin the sludge, calcining the same under-con itions capable of reducing at least a considerable proportion of the calcium sulfate content thereof, and leaching the calcined material with a liquid capable of removing the alkalinev earth metal sulfur-compounds therefrom.

In testimony whereof I aiiix my signature in presence of two witnesses. y

ADDISON F. HOFFMAN.

Witnesses JENNIE JONES, B. 1F. FUNK. 

